Illustrations

8.1
When you change the mass, the momentum does not change, but rather stays the same. As the force applied is being changed, the momentum also changes. All of this can be explained on the force vs. time graph.

8.2
As the mass increases the kinetic energy increases, and as the mass decreases the kinetic energy decreases. Also, when the mass is changed the speed also changes.

8.3
Forces are always equal but opposite so therefore, if the momentum of one object increases, the other object's momentum decreases. The sum of the impulses of the balls is equal to zero.